The picolinic acid class of herbicides comprise a substituted 2-pyridine carboxylic acid group and their ester and salt derivatives. The picolinic acid group of herbicides is used in control of perennial broad leaf weeds by pre emergent application to soil and post emergent foliar or soil application. They are useful in control of broadleaf weeds in grasses.
Examples of picolinic herbicidal compounds include compounds of formula (I)
whereinX1 and X2 are independently selected from hydrogen, chloro and amino; andR is an ester or salt counter ion.
Specific examples of known picolinic acid herbicides include aminopyralid (4-amino-3,6-dichloropyridine-2-carboxylic acid) its esters and salts, picloram (4-amino-3,5,6-trichloropyridine-2-carboxylic acid also referred to as 4-amino-3,4,6-trichloropicolinic acid) its salts and esters and clopyralid (3,6-dichloropyridine-2-carboxylic acid also called 3,6-dichloropicolinic acid) its salts and esters.
The amine salts of the picolinic acid herbicides are in many cases water soluble and aqueous formulations of the amine salts are convenient to use. At the site of use the concentrate formulations can conveniently be diluted in a spray tank for soil or foliar application.
One of the significant limitations of amine salt compositions is their stability, particularly at high loadings. The poor solution stability is particularly a problem for low temperature storage of highly concentrated solutions, for example of at least 300 g/L and particularly at least 500 g/L (based on active acid equivalent). This places limitations on the storage and handling of the herbicidal picolinic acid amine salts with the result that the loading of salt needs to be lower than would normally be stable due to the propensity to form a significant proportion of crystalline deposits at low temperature which are not always readily redissolved.
The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application.